I used 5 magnets, 20x10x3 (nominal size). I bought them on AliExpress here. But it's not a rare staff, you know.

Ok, here is the point: 5 magnets on single metal strip, locked in the printed holder. The holder ribs are required for prevent the bits flipping.

For grouping the magnets I used a metal strip of 0.3mm thickness. You can make this thing without the common strip, but I think it can be a bit awkward. And probably you'll need to configure the thing for the less thickness of the magnets. How to configure, see below.

I glued the holder to the adhesive tape, but there is also an option to screw it on.

Printing disclaimer

You must have a well calibrated printer including correct flow setting for the filament which you suppose to use. The printing tolerance - 0.15mm.

If you're not sure or didn't understand what I'm talking about - don't waste the time to make this thing. Or don't blame me after all that your printed parts don't fit together.

Also in some cases you'll need to use the tools (needle files for corners, drill bits for holes and etc.) to reach the best result from the printed model. Especially if use don't use Junction Deviation or Linear Advance. You shouldn't expect that the model will be fine immediately from the printer. At least not always :)

Source

The source is here.

How to use my configurable models in OnShape

To get an access to the thing source you'll need an account in OnShape. It can be free, so made it for yourself.

Go to the document by the specified link.

Go to the tab "print setup". There should be a few configurable values in the upper-left corner. Change what you need. Wait while rendering finished then export parts from this tab (see in the bottom-left corner). They already oriented in the best printing position.